1. Field of the Invention
The present invention relates to a method and a system for a communication node with a plurality of network interfaces.
2. Discussion of the Background
Communication networks and communication nodes for communication over communication networks are being produced, installed and operated in many diverse forms. Communication networks can be operated, for example, on Ethernet networks, on PSTN networks (PSTN: Public Switched Telephone Network), on mobile radio networks such as GSM or UMTS mobile radio networks (GSM: Global System for Mobile Communications, UMTS: Universal Mobile Telecommunications System), on wireless WLAN networks (WLAN: Wireless Local Area Network), on radio networks, which are operated according to the WiMAX standard (WiMAX: Worldwide Interoperability for Microwave Access), on networks which are operated according to the UWB (UWB: Ultra Wide Band) technology, on IP networks (IP: Internet Protocol), on ATM networks (ATM: Asynchronous Transfer Mode) or on Bluetooth networks. Of course, many diverse methods for data transmission can be used in such networks, such as, for example, a HSDPA method (HSDPA: High Speed Downlink Packet Access) in a UMTS network. A communication node can relate, for example, to a fixed installed computer, to a mobile radio terminal, to a communication relaying device such as a network router, or to a mobile computer, such as a notebook. In communication between communication nodes, a plurality of diverse problems must be solved, such as, for instance, reliability, speed, security, efficiency, etc. It is of advantage to structure these problems according to the OSI reference model (OSI: Open Systems Interconnection), for example, or according to the TCP/IP reference model. These reference models have a plurality of layers configured one on top of the other (OSI reference model: 7 layers, TCP/IP reference model: 4 layers), each layer being assigned certain functions. In the OSI reference model, the seven layers are a bit transmission layer (layer 1, a physical), a security layer (layer 2, data link), a relaying layer (layer 3, network), a transport layer (layer 4, transport), a session layer (layer 5, session), a presentation layer (layer 6, presentation) and an application layer (layer 7, application). The TCP/IP reference model, on the other hand, includes 4 layers, a network access layer (OSI layer 1-2, for example Ethernet), an Internet layer (OSI layer 3, IPv4, IPv6), a transport layer (OSI layer 4, TCP) and an application layer (OSI layer 5-7, for example HTTP).
A communication node has in each case at least one network interface. Such a network interface can relate, for example, to an Ethernet interface for connection to an Ethernet network, to a WLAN interface for connection to a WLAN network, or to a GSM interface for connection to a GSM mobile radio network. Depending upon the function of the communication node, the communication node has at its disposal a plurality of network interfaces. Thus a network router can have at its disposal a plurality of same-type Ethernet interfaces, or a notebook can have an Ethernet interface, a WLAN interface and a GSM interface. In particular, with mobile communication nodes, the network interfaces of the communication node must be constantly adapted to changing requirements. Thus, with private use, a communication node can be connected to the Internet via a PSTN network, for example, with use at a public location, it can be connected to the Internet via a public WLAN network, with use in a train, it can be connected to the Internet via a GSM mobile radio network, and with use in a company place of work, it can be connected to the Internet via a company-internal Ethernet network. Network parameters, such as, for example, the IP address of the communication node, must thereby be re-configured for each of these locations. In particular, the communication node thus appears in the Internet each time with a different IP address, and it is therefore not possible, for example, following a change of location of the mobile communication node, to continue to access the mobile communication node from another communication node. This problem becomes apparent with a VoIP (VoIP: Voice over IP) connection between a first communication node and a mobile communication node. With a change of the connection of the mobile communication node, for example, from a WLAN network to an Ethernet network, a new IP address is assigned to the mobile communication node. However, this assignment of a new IP address is not automatically transmitted to the first communication node, so that the first communication node is subsequently no longer able to further contact the mobile communication node, and an existing VoIP has to be interrupted, for example.
In the state of the art, solutions are known, such as, for example, mobile IP, dynamic DNS (DNS: Domain Name System) or SIP (SIP: Session Initiation Protocol), for improving the IP connectivity of mobile communication nodes. Mobile IP protocol is defined in this way by the IETF (IETF: Internet Engineering Task Force) in the RFC 2002 (RFC: Request for Comment). According to the mobile IP protocol, the mobile communication node is assigned a constantly available home address, which is configured on a constantly available network server (the so-called home agent). With a connection to a communication network or with a change between communication networks, a dynamic IP address is assigned to the communication node. This dynamically assigned IP address is designated as care-of address in mobile IP. The care-of address is then assigned to the constantly available network server of the home address. This assignment makes it possible for the mobile communication node to be always contactable, regardless of the current location, via access to the home address in that the constantly available network server forwards queries to the home address automatically to the momentary care-of address. A drawback of the mobile IP is that the assignment of a care-of address and the subsequent allocation between the home address and the care-of address on the network server can take a relatively long time, and therefore a connection may be truncated. A further disadvantage is that with an outgoing connection from the mobile communication node, the care-of address is normally used, and therefore, after a change of location, such a connection must be re-established based on a new care-of address.
Also defined by the IETF was the Internet draft “Host Identity Protocol Architecture”. This Internet draft originated from the problem that two functions are simultaneously assigned to an IP address. Identified with the IP address at the same time is a communication node (or more precisely a network interface of the communication node), and the location of this communication node is identified. The IP address is a dynamic identifier for a communication node, and corresponds to a “location” in the topology of the Internet (based on the IP address). That means that the IP address of the communication node changes when the location changes. The IP address is used at the same time as a static identifier of the communication node, which is independent of the topology. With the HIP architecture (HIP: Host Identity Protocol), a separation is made possible between the function of an IP address as identifier of a communication node and the function of an IP address as identifier of the location of this communication node. In addition, a host identifier is assigned to a communication node having a network interface and an IP address. The host identifier can be generated locally on the communication node as a statically unambiguous name, a host identity tag of 128 bits being generated from the host identifier by means of a hash function. The IP address of the network interface of the communication node is assigned to the host identity tag. The transport layer protocols such as TCP and UDP are subsequently connected to the host identities (instead of to IP addresses), so that connection questions concerning a communication node always take place via a host identity. The assignment of a host identity tag to an IP address can be continuously updated in special, constantly available directories, the so-called rendezvous server. A drawback of this method is that no mechanisms are provided to make possible a dynamic connection of a communication node to a plurality of network interfaces.
Described in the European patent EP 1 271 896 is a method for mobile IP nodes in heterogeneous networks, a dynamic IP care-of address being assigned to an IP home address of a mobile communication node, and the IP care-of address indicating the current location of the mobile communication node. An interface administration module sets up a look-up table with available network interfaces of the communication node. Applications access a virtual IP network interface, the virtual IP network interface being connected to a network interface via the interface administration module, and, with a change of the network interface of the mobile communication node, the connection of the virtual IP network interface to a network interface is updated by means of the interface administration module, based on the look-up table. A drawback of this method is that only one mobile IP-based technology is able to be used, and new technologies, such as, for example, the HIP, are not able to be used. A further drawback of this method is that it becomes difficult for the operator of the communication networks to carry out resource management.